Adherent cells such as somatic cells adhere to the bottom surface of a culture vessel and form a foothold before repeating cell division and cell elongation to increase the number thereof. In this regard, if the increase in the cell number keeps going on, the cells start to scramble for adhesion area on the bottom surface of the vessel since the cells remain adhered to the bottom surface of the culture vessel. Therefore, if the increase in the cell number continues, there will be no space between the cells and eventually the cells will be multi-layered, due to which the cells will suffocate without sufficient nutrients (confluent condition) and result in dead cells.
Accordingly, when adherent cells are cultured in a culture vessel, culture needs to be performed while detaching the cells from the culture vessel and transferring them to other vessel at a given cell number (given density) before reaching the confluent condition so as to keep sufficient nutrients to go throughout the adherent cells (subculture).
In order to detach the cells from the culture vessel and transfer them into other vessel, there is a need to use an enzyme solution such as trypsin to degrade the cell adhesion protein to allow the cells to float or use a scraper to physically detach the cells from the culture vessel. In the field of cell culture, it is well known that these methods are unfavorable treatments since they will place stress on the cells. For example, trypsin is known to be toxic to cells and it is known that a trypsin treatment will change the property of the cells and result dead cells. Therefore, it is desirable to minimize such treatments as much as possible that will place stress on cells.
In addition, the operation of detaching adherent cells from a culture vessel and transferring them into other vessel is manually conducted in a clean bench. Manual operations are constantly at a risk of contamination.